Condenser motor



Nov. 3, 1942.

E. B. SLEETER coNDENsER MOTOR Filed NOV. 29, 1939 l INVENToR fdwczrd. Sfeeer ATTORN EYS Patented Nov. 3, 1942 CONDENSER MOTOR Edward B. Sleeter, Dayton, Ohio, assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware Application November 29, 1939, Serial No. 306,633

Claims.

This invention relates to electric motors of the condenser-start type, and has for an object to improve the operating characteristics of the same.

In a condenser-start motor, it has been obopened after completing the starting function.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accom- 5 panying drawing wherein a. preferred embodiserved that a residual charge is left in the star'tment of the present invention is clearly shown. ing condenser which will discharge through the In the drawing, the single figure illustrates motor winding after the motor is disconnected diagrammatically the elements and features of from the line and hasslowed down sufiiciently the herein described control circuit. for the centrifugal switch to close. That dis- The leads of a power line are indicated at Il) charge causes the motor to act as a self excited and I2 one of which is connected with a line generator, and results in the motor being noisy switch I4. The motor comprises a main windin stopping in that it slows down with somewhat ing I6 connected across the line to the motor of a grunt. It has likewise been observed that terminals i8 and 20, and a phase or starting a voltage is generated at the motor terminals l5 winding 22 having connection with the motor which may adversely aect the operation of other terminal I8. A lead 24 connects the winding 22 apparatus, such as relays, solenoid valves and with a fixed contact 26 of an automatic switchthe like, that may be connected in parallel with ing mechanism 28. From the terminal 20, a lead the motor. When that occurs in oil burning in- 30 connects with a terminal 32 of a motor startstallations it is very objectionable and in the ing condenser 34, the opposite terminal 36 of same instances may be hazardous, in that the which is joined to a second fixed contact 38 of solenoid valve might be left partially open, perthe automatic switch 28 by means of a connecmitting leakage. tor 40.

It is therefore a further object of this inven- The automatic switching mechanism 28 distion to effect a substantially complete discharge zo closed illustrates a centrifugal or speed responof the starting condenser before the motor is sive switch providing a bridging contact 42 spring disconnected from the line. urged at a condition of rest to cross connect the Another object of the invention is to prevent fixed terminals 26 and 38. As illustrated, the the residual charge of a condenser from disautomatic switch comprises fiyweights or like charging through the motor windings when the 30 devices 44 urged inwardly by Spring 45 and all motor is disconnected from the line and the cencarried by a motor shaft 48 upon which is trifugal switch closes. mounted the usual rotor 50. As the rotor ap- A further object of the invention is to prevent proximates a predetermined or designed speed, the motor from acting temporarily as a self exthe centrifugal mechanism operates to open the cited generator after it is disconnected from the circuit connection between the fixed contacts 26 line. and 38 as is the usual function of such devices,

A further object is to eliminate noise of opand as is well known to those experienced in eration as the motor slows down and comes to the art. rest. While it is illustrated that the automatic A further object of the invention is to prevent 4U switch 28 comprises a centrifugal or speed rethe generation of energy during stopping of a sponsive mechanism, it is contemplated that condenser start motor that will adversely affect Other automatic switching means operating for the operation of associated apparatus. the same functions may be used, and that the A still further object yis to substantially dissiexpression automatic switching mechanism conpate the residual charge of a motor starting contemplates magnetically operated switches and denser within a short time after disconnecting thermal current switches and the like that may the same from the circuit, without discharging be used in the same capacity. the same through the motor windings upon re- As is well known to those experienced in the closingof the automatic switch. art, the use of the condenser 34 is for the pur- The foregoing objects of the invention are acp ose of producing a difference in phase between complished, and the objections stated are elimthe currents flowing in the windings of the motor inated by placing a resistance across the starting so as to facilitate self starting of the motor imcondenser so as to dissipate its charge while the mediately that the line switch I4 is closed. When motor is running, and within an appreciably the motor is started, and the speed of the rotor short time after the automatic switch has been is in-approxmation 0f that Speed for which the Vmotor is designed, the automatic switching mechanism 28, regardless of its specific characterization, operates to eliminate the phase winding from the motor circuit, such that the motor thereafter operates wholly in response to the energy impressed upon the main winding I8. In other words, the series connection between the phase winding 22 and the condenser 3l is opened and the condenser 34 is left with a residual charge, the magnitude of which depends upon the point on the impressed voltage wave at which the circuit is opened, and only one of its plates or electrodes connected. Normally, the con-` denser in this condition is incapable of discharging, but holds its charge in suspension so to speak, until reclosing of the automatic switch, or until some other return connection is made. It appears to be this discharge of the residual charge of the condenser upon reestablishing the second connection, as when the motor slows down for stopping, that gives rise to the objections hereinbefore mentioned.

To eliminate those objections a resistor 52, preferably of the non-inductive type, is connected to the terminals 32 and 38, or in other words shunted across the condenser 34, which permits the condenser within a reasonably short time after disconnection from the phase winding to become sufficiently discharged while the motor is running, and without introducing any of the objections stated. The resistor should be of sufficiently high resistance so as not to effect the starting torque of the motor, but not too high to discharge the condenser within the required, or within a reasonably short time. As one example, u

It is well known that a condenser is discharged through a resistor connected across its terminals 1n accordance with the following, where z H RF Substituting assumed values then 2o z 1 e .MIR

Transposing and solving.

l i-QT e.0001R Q001H log e log 1U R 86,900 ohms This means that under the assumed conditions the condenser 34 would be 90% discharged in a period of twenty seconds from the instant that the automatic switch 28 opens the series connection between the condenser 34 and the phase winding 22. It has been found that discharge of the condenser under those conditions, and within that time is usually suficient'forall practical purposes, and that the residual charge of the condenser will have then been sufficiently dissipated so as not to adversely affect mechanism connected in association with the motor, and will eliminate objectionable noise in stopping.

While the embodiment of the present invention as herein disclosed, constitutes a preferred form, it is to be understood that other forms might be adopted, all coming within the scope of the claims which follow.

What is claimed is as follows:

1. In a capacitor start motor in combination, a main circuit, and an auxiliary circuit for starting purposes,.means for energizing and deenergizing both circuits coincidentally, said auxiliary circuit comprising a phase winding, a disconnecting switch and a condenser in series all connected across the main circuit, said disconnecting switch operating independently in response to speed to open said auxiliary circuit, and said condenser being permanently shunted by a resistor of such magnitude as to effect gradual but substantial discharge of the condenser after the auxiliary circuit has been opened, whereby the motor is prevented from acting as a self excited generator after being disconnected from the line, and with the auxiliary circuit closed.

2. In a capacitor motor, a main winding for the motor, means for energizing and deenergiz ing the main winding, an auxiliary starting winding connected in series with a switch and a condenser across the main winding so as to be energized and deenergized therewith, said condenser being permanently shunted by a high resistance discharge resistor, and means responsive to the speed of the motor for opening the switch above a certain speed.

3. In a condenser start motor, a main stator winding, a phase winding, means for energizing and deenergizing both of said windings, a condenser in series with said phase winding, a high resistance discharge resistor shunted around the condenser, and means responsive to motor speed for disconnecting the phase winding, the con denser and the resistor during running of the motor.

4. In a condenser start motor, a main stator winding, a phase winding, means for energizing and deenergizing both of said windings, a condenser, a normally ciosed switch connecting the condenser in series with the phase winding, a high resistance discharge resistor connected in shunt about the condenser and adapted to dissi' pate any effect of the condenser after the phase winding circuit has been interrupted, and means actuated by the motor at a predetermined speed thereof to open the switch and render the phase winding and condenser ineffective.

5. In a condenser start motor having two terminals adapted to be connected to a source of electric energy; a running winding connected across the two motor terminals; a starting winding connected across said two motor terminals; a condenser in circuit with the starting winding, a normally closed switch in the starting winding circuit between the condenser and the starting Winding, a high resistance discharge resistor connected in shunt about the condenser, and centrifugal means actuated by the motor for opening the switch to interrupt the starting winding circuit including the condenser during the running operation of the motor.

EDWARD B. SLEETER. 

